Radiators Not Heating Up? Here Is What to Check

One radiator is cold at the top

Air trapped in the radiator prevents hot water from filling it completely. Bleed the radiator using a radiator key - turn the bleed valve anticlockwise until you hear air hissing out, then close it as soon as water starts to drip. Check your boiler pressure afterwards and top it up if it has dropped below 1 bar.

One radiator is cold at the bottom

Cold at the bottom means sludge has settled inside the radiator, blocking the flow of hot water. Bleeding will not fix this. The radiator needs to be removed and flushed, or the whole system needs a power flush to clear the sludge out properly.

Radiators downstairs work but upstairs do not

This usually means the boiler pump is not strong enough to push water to the upper floors, or there is a circulation problem. Check that the pump is running - you should be able to feel a slight vibration. If it is silent, it may have seized. This needs an engineer.

All radiators are lukewarm

If none of your radiators are getting properly hot, the boiler itself may be the issue. Check the boiler pressure, check for error codes, and make sure the thermostat is set correctly. If everything looks fine on the controls but the radiators are still lukewarm, the heat exchanger may be failing or the system may need a power flush.

The thermostatic valve is stuck

Thermostatic radiator valves (TRVs) can stick in the closed position, especially if they have not been used for a while. Remove the TRV head and check if the pin underneath moves freely up and down. If it is stuck, tap it gently or apply a small amount of WD-40. If it will not budge, the valve needs replacing.